1. Field of the Invention
This invention relates to orbital polishing and, more particularly, to a method for forming restrictive tooling used with orbital polishing machining.
2. Background Art
Abrasive flow machining is a well-known, nontraditional machining process whereby""a visco-elastic media, permeated with an abrasive grit, is extruded through or past a workpiece surface to abrade that surface. The abrasive action in abrasive flow machining can be thought of as analogous to a filing, grinding, lapping, or honing operation where the extruded visco-elastic abrasive media passes through or past the workpiece as a xe2x80x9cplugxe2x80x9d. The plug then becomes a self-forming file, grinding stone, or lap as it is extruded under pressure through the confined passageway restricting its flow, thereby abrasively working the selected surfaces of the workpiece. Recently, this technology has been utilized with orbital polishings to create a hybrid technology. Orbital polishing uses much of the same technology as the abrasive flow machining (AFM) process, but adds a mechanical motion to polish three-dimensional forms not possible to be polished by a conventional abrasive flow machining. While AFM requires flow of abrasive media over the workpiece, such flow may or may not be used with the orbital polishing process, since motion is imparted to the abrasive media by the orbital polishing machine independent of any abrasive media flow. Details of an orbital polishing machine may be found in U.S. Pat. No. 4,891,916, which is incorporated herein by reference.
FIG. 1 shows a schematic view of the polishing process using an orbital polishing machine 10. The machine 10 has a first platen 15 upon which a workpiece 20 is secured and a second platen 25 upon which restrictive tooling 30 is secured. Media 35 is introduced between the restrictive tooling 30 and the workpiece 20. When compressed and subjected to elevated pressures, the media 35 forms a mirror image of the workpiece 20 and the restrictive tooling 30 as it conforms to the geometry as a high viscosity elastic fluid. The transfer to an elastic stage helps the media 35 keep the shape of the restrictive tooling 30 and acts as a three-dimensional grinding stone. The first platen 15 and the second platen 25 are then translated relative to one another to produce relative motion between the workpiece 20 and the tooling 30. Preferably, the media 35 adheres to the tooling 30 and slides across the workpiece 20, thereby providing an abrading motion of the media 35 over the face of the workpiece 20.
Using the orbital polishing machining process, the media 35 may be held captive in a vessel 40 between the workpiece 20 and tooling 30 so the only motion of the media 35 is produced by the relative motion of the platens 15, 25 or, as previously mentioned, additional motion may be produced by circulating the media 35 under pressure between the workpiece 20 and the tooling 30. This also acts to exchange the abrasive media 35 at the surface of the workpiece 20 replacing media 35 which is worn, charged with workpiece material or heated (due to elastic and plastic deformation and function) with fresh media at the working surface.
The media employed for orbital polishing is similar to that used in the AFM process. Compared to the media used in the AFM process, the media used in orbital polishing is typically made of a combination of visco-elastic polymer having a higher viscosity with a higher abrasive concentration. While any number of different abrasive media may be used for such polishing, silicon carbide abrasive is most commonly used. Boron carbide and diamond abrasive media are typically used for polishing hard materials and/or for achieving an extremely fine surface finish. However, one of many other abrasives known to those skilled in the art of abrasive materials may be used.
Restrictive tooling is commonly constructed by conventional machining methods or by casting. The preferred material for the restrictive tooling is pressure-molded nylon or polyurethane. Steel or aluminum tools are normally less desirable due to the cost, the weight, the machining difficulty to produce them, and their performance in the polishing process. When the restrictive tooling is made of nylon or polyurethane, the abrasive media tends to adhere to restrictive tooling rather than to the workpiece. However, polyurethane restrictive tooling normally requires shaping to create the required gap and also exhibits only moderate wear resistance. Nylon tooling, on the other hand, offers greater wear resistance but requires machining which can detract from the time saving offered by the orbital polishing process.
The restrictive tooling 30 for orbital polishing must be constructed to create a restriction in three-dimensional parts. When restrictive tooling is required, tooling is constructed to be the offset mirror image of the workpiece 20. The clearance between the workpiece 20 and the restrictive tooling 30 is provided for the media 35 layer to simulate a flexible grinding stone effect as well as to accommodate the orbital motion.
The orbital amplitude of the polishing machine determines the movement of the cutting edges embedded in the media. Larger amplitudes yield larger movement of the cutting edges which encourage larger material removal. However, as will be explained in more detail, the orbital amplitude should not be larger than the minimum concave or internal geometry of the workpiece. Smaller orbital amplitudes decrease the relative motion of the abrasive cutting edges against the workpiece. These two limitations define the geometrical limitations of the application of the orbital polishing process.
Nevertheless, for orbital polishing to be successful, it is very important that the restrictive tooling be formed to be the approximate mirror image of the workpiece to create a uniform gap between the workpiece and the restrictive tooling in which the abrasive media may rest. This uniform gap is important because a media of uniform thickness across the face of the workpiece provides a uniform force against the workpiece by the tooling.
Once the restrictive tooling is fabricated, it must then be properly mounted upon the orbital polishing machine so that it is properly aligned with the associated workpiece.
One object of the present invention is to provide a method and an apparatus for producing restrictive tooling using a simple and effective process that provides such tooling in a relatively short period of time.
Another object of the present invention is to permit the fabrication of restrictive tooling using a workpiece mounted upon an orbital polishing machine and then to use the same restrictive tooling on the same orbital polishing machine to polish the workpiece.
Still other objects of the present invention will become apparent to those of ordinary skill in the art upon reading and understanding the following detailed description.
One embodiment of the subject invention is directed to a method for producing, from a blank, restrictive tooling for use with a flowable abrasive media upon a workpiece in an orbital polishing machine wherein the workpiece has a particular contour, the method comprising the step of urging one of either the workpiece or the blank along a predetermined path against the other to physically impart a proportioned contour of the workpiece into the blank thereby producing the restrictive tooling within the blank.
The relative motion between the workpiece and the blank may be any oscillatory motion, including translational, orbital, gyrating, linear or reciprocating motion.
This method may further comprise the intermediate steps of: (a) producing a first molded body using the contoured blank as the pattern, whereby the first molded body is a negative image of the contoured blank; and (b) producing a second molded body using the first molded body as the pattern, whereby the second molded body is a negative image of the first molded body and duplicates the shape of the contoured blank and whereby the second molded body may be used as the restrictive tooling.
Another embodiment is directed to a method using an orbital polishing machine for producing restrictive tooling that may be used in an orbital grinding operation comprised of the steps of:
a) mounting upon a first platen of an orbital grinding machine a workpiece;
b) mounting upon an opposing second platen of the orbital grinding machine a blank made of a material softer than that of the workpiece;
c) energizing the orbital grinding machine to produce relative motion between the workpiece and the blank;
d) advancing the first platen and the second platen toward each other until the workpiece penetrates the blank a predetermined depth to define a cavity or xe2x80x9ccorexe2x80x9d; and
e) after the cavity has been formed, retracting the first platen and the second platen from each other.
Yet another embodiment is directed to a method of producing and utilizing restrictive tooling for an orbital polishing operation further comprised of the additional steps of:
f) applying a layer of abrasive media associated with orbital polishing between the workpiece and the tooling;
g) advancing the first platen and the second platen toward each other until the blank and tooling are separated a predetermined distance; and
h) energizing the orbital polishing machine to create relative motion between the abrasive media and the workpiece to polish the workpiece.
Still another embodiment is directed to restrictive tooling produced by the method comprising the step of urging one of either or both the workpiece or the blank along a predetermined path against one another to physically impart a proportioned contour of the workpiece into the blank thereby producing the restrictive tooling.
It is possible to utilize a single orbital polishing machine to both produce restrictive tooling using a workpiece and then to subsequently polish that workpiece using the same restrictive tooling.